1. Field of the Invention
The present invention relates to an electrode assembly and an battery cell, and methods of manufacturing the same, and more particularly, to an electrode assembly and a battery cell having various shapes, and methods of manufacturing the same.
2. Description of the Related Art
With technical advancements and increasing demand for mobile devices, demand for rechargeable batteries has sharply increased. Among rechargeable batteries, lithium secondary batteries with high degrees of energy density and high operating voltages, as well as superior life cycles are widely used as energy sources for various electronic appliances as well as a variety of mobile devices.
Generally, a lithium secondary battery is formed to have a structure in which an electrode assembly and an electrolyte are sealed within a battery case, and may be classified as a cylindrical-type battery, a prismatic-type battery, a pouch-type battery, or the like according to the appearance thereof, or may be classified as a lithium ion battery, a lithium ion polymer battery, a lithium polymer battery, or the like, according to the type of electrolyte used therein. Due to the recent trend for the miniaturization of mobile devices, the demand for thin prismatic batteries and pouch-type batteries has increased, and particularly, interest in lightweight pouch-type batteries having shapes that are easy to change is high.
The electrode assembly received in the battery case may be classified as a jelly-roll (wound)-type, a stacked (laminated)-type, and a stacked and folded (composite)-type according to the shape thereof. The jelly-roll-type electrode assembly is manufactured by coating metal foil used as a current collector with an electrode active material, pressing the coated metal foil, cutting the pressed metal foil in a band form having a desired length and width, separating a negative electrode sheet and a positive electrode sheet using a separator film, and winding the negative and positive electrode sheets and the separator film in a spiral form. In the jelly-roll-type electrode assembly, since an excessive amount of stress may be generated from a curved electrode surface due to a small radius of gyration in a central portion of the spiral form, electrode delamination may be easily generated. Such electrode delamination may facilitate an extraction of lithium metal crystals from an electrode during charging and discharging of the electrode to cause a reduction in battery lifespan, thereby degrading battery stability.
Meanwhile, the stacked-type electrode assembly is an electrode assembly, manufactured in a manner in which a negative electrode, a separator, and a positive electrode are vertically stacked. The stacked and folded-type electrode assembly is an electrode assembly, manufactured by winding or folding a single electrode or stacked electrode bodies respectively formed of a negative electrode, a separator, and a positive electrode using a long sheet-type separator.
Recently, in accordance with increasing demand for mobile devices having various designs, battery cells having various shapes are also required, such that the development of battery cells having various shapes, rather than the related art quadrangular shapes, for example, a battery cell having a curved portion, are being attempted. However, in order to mass produce such various battery cells, several technical limitations need to be solved. One aspect of the limitations relates to the processing of a separator interposed between electrodes or a sheet-type separation film enclosing a unit cell. In general, since a negative electrode or a positive electrode may be manufactured by coating a current collector formed of a solid material such as a metal, with an electrode active material, the electrode may be easily cut to have a desired shape using a mold or the like. However, since the separator or the separation film may have a reduced thickness in a range of about 10 to 30 μm and be formed of a soft material such as a polyester, when the film is cut using a mold or the like, it is difficult to precisely cut the film in a desired shape, abrasion of the mold is rapidly generated, a lowering in productivity is caused, and manufacturing costs are increased. Meanwhile, in a case in which shapes of the electrode and the separator and/or the separation film do not coincide with each other and thus, the separator and/or the separation film is present on a portion on which the electrode is not present, when the electrode assembly is inserted in an battery case, a separate space for receiving the separator and/or the separation film is required to cause obstruction in implementing a desired battery design.
Thus, in order to realize battery cells having various shapes, the development of technology enabling the processing of the separator and/or the separation film so as to coincide with the shape of the electrode assembly has been demanded.